The present invention relates to improvements in a device for driving printing rings in a printer having the printing rings each rotatably supported by a swingable lever adapted to be swung about its pivot axis so as to move the respective printing ring in an arcuate path around the pivot axis toward and against a platen for printing onto a paper therebetween a selected character of the respective printing ring selected for the printing operation during the rotation thereof.
A printer of the type described above has a plurality of printing rings each provided on the periphery thereof a plurality of printing characters and each rotated about its own axis by a driving source, the respective printing ring being supported by a swingable lever pivoted about a pivot axis so that the respective printing ring is selectively moved in an arcuate path from a normally held inoperative position toward and against a platen around the pivot axis by a printing character selection command from a control circuit of the printer so as to print onto a paper held therebetween a selected printing character on the printing ring selected during the rotation of the printing ring. An electric motor is usually used in rotating the respective printing rings while a spring is used in swinging the respective swingable lever supporting the rotating printing ring wherein the printing ring is rollingly moved toward and away from the platen during the swinging movement of the lever by the engagement of a gear rotated about the pivot axis of the lever with a gear integral and coaxial with the printing ring for rotating the printing ring about its axis.
In the prior art printer of the type described above, since an electric motor is used as the driving source for rotating the respective printing rings, the respective printing rings are rotated at all times during the operation of the printer. Therefore, in swinging the swingable lever selectively upon receipt of a printing character selection command from the control circuit for the printing operation, the peripheral speed of rotation of the respective printing ring about its axis is made equal but in opposite direction to the peripheral speed of the printing ring caused by the rolling movement thereof along the arcuate path around the pivot axis of the swingable lever so that the resultant peripheral speed of the respective printing ring is rendered to be zero when the printing ring abuts against the platen for the printing thereby aiming at insuring the exact printing of the selected character. However, since complicated construction is required in achieving the above described operation in the prior art printer, false positioning of the selected character with respect to the paper or false selection of the character could not be avoided in the prior art printer.
The present invention aims at avoiding the disadvantages of the prior art printer as described above.